The present invention relates to manufacturing methods and apparatuses of an optical device and a reflection plate each of which is provided with a resin thin film having a micro-asperity pattern.
In this specification, “micro-asperity pattern” is a generic term of asperity shapes that develop one-dimensionally or two-dimensionally and is 0.1 μm to hundreds of micrometers in depth and arbitrary in width, length, and shape. And “reflection-type liquid crystal display device” is a generic term of devices in which a liquid crystal is sealed between a transparent counter substrate having a transparent electrode and an active matrix substrate having a reflection surface that is provided with a surface micro-asperity pattern.
Nowadays, liquid crystal display devices are increasingly applied to personal computers, TV receivers, word processors, video equipment, etc. On the other hand, to increase the functionality and reduce the size, power consumption, cost, etc. of such electronic equipment, reflection-type liquid crystal display devices are being developed that display an image by reflecting external light instead of using a backlight.
FIG. 19 shows an example of such reflection-type liquid crystal display devices. A reflection plate 1 is disposed under a counter substrate 28 that is composed of a transparent electrode facing a liquid crystal layer 27, a color filter layer formed over the transparent electrode, a surface glass substrate disposed over the color filter layer, and other members. The reflection plate 1 is used to increase the viewing angle of image display of the liquid crystal display device by diffuse-reflecting light coming from the counter substrate 28.
As shown in FIG. 20, the reflection plate used in this liquid crystal display device is formed in the following manner. A resin thin film 4 is formed by applying, by spin coating or the like, resin in which polymerization reaction has almost completed to the surface of a substrate 5 made of glass or resin or the surface of a structure in which TFT transistors, liquid crystal driving elements, etc. are formed on such a substrate. The resin thin film 4 is melted by heating it and a micro-asperity pattern stamper 33 is pressed against the resin thin film 4 that is formed on the substrate 5, whereby a micro-asperity pattern is formed.
However, when polymerized resin in which polymerization reaction has almost completed is melted, resulting flowability is low and a stress variation is caused in the thin film 4 by the pressing with the stamper 33. Internal stress develops as the thin film 4 is set thermally. As shown in FIG. 19, in the reflection plate 1, an alignment film (insulating film) 36 needs to be formed on the top surface of a reflection film 26. To this end, baking needs to be performed at about 200° C.
The alignment film 36 is necessary to control liquid crystal molecules so that they have an arrangement and an inclination that are suitable for a liquid crystal operation mode as well as to insulate the reflection film 26 (metal coating) from the liquid crystal layer 27. For example, the alignment film 36 is required to be applied uniformly, be strong enough to endure a rubbing process, exhibit high adhesiveness when brought into contact with an ITO film, TFTs, interconnections, or the like, and be stable when exposed to chemicals used in a cleaning process or subjected to a heat treatment.
Polyimide is used conventionally as a resin material that satisfies that above requirements. Polyimide has high heat resistance (about 300°), is transparent and has a high glass-transition temperature, does not react with liquid crystals, is high in the affinity for liquid crystals, aligns liquid crystals easily, and exhibits high adhesiveness when brought into contact with an ITO film, TFTs, interconnections, or the like.
Therefore, if baking is performed for the alignment film 36 that is made of polyimide which has high heat resistance and a high glass-transition temperature after a micro-asperity pattern was formed by using a resin that has a low glass-transition temperature and low heat resistance and in which polymerization reaction did not complete and then the reflection film 26 was formed, a problem arises that the micro-asperity pattern loses its shape in the baking process.